Analysis of One‐Bond Se‐Se Nuclear Couplings in Diselenides and 1,2‐Diselenoles on the Basis of Molecular Orbital Theory: Torsional Angular Dependence, Electron Density Influence, and Origin in 1J(Se, Se)

Nuclear couplings for the Se-Se bonds, 1 J (Se, Se), are analyzed on the basis of the molecular orbital (MO) theory. The values are calculated by employing the triple ζ basis sets of the Slater type at the DFT level. 1 J (Se, Se) are calculated modeled by MeSeSeMe ( 1a ), which shows the typical torsional angular dependence on ϕ (C Me SeSeC Me ). The dependence explains well the observed 1 J obsd (Se, Se) of small values (≤ 64 Hz) for RSeSeR′ ( 1 ) (simple derivatives of 1a ) and large values (330–380 Hz) observed for 4-substituted naphto[1,8- c , d ]-1,2-diselenoles ( 2 ) which correspond to symperiplanar diselenides. 1 J (Se, Se: 2 ) becomes larger as the electron density on Se increases. The paramagnetic spin-orbit terms contribute predominantly. The contributions are evaluated separately from each MO ( ψ i ) and each ψ i → ψ a transition, where ψ i and ψ a are occupied and unoccupied MO's, respectively. The separate evaluation enables us to recognize and visualize the origin and the mechanism of the couplings.